1. Field of the Invention
The present invention relates to a method and apparatus for detecting a missing nozzle in an inkjet printhead, and more particularly, to a method and apparatus for detecting a missing nozzle in a thermal inkjet printhead.
2. Description of the Related Art
In general, inkjet printheads are devices that eject ink droplets onto desired positions of a recording medium to form an image of a predetermined color. Inkjet printheads are categorized into two types according to the ink ejection mechanism thereof. The first one is a thermal inkjet printhead that ejects ink droplets due to an expansion force of bubbles generated in ink by thermal energy. The other one is a piezoelectric inkjet printhead that ejects ink droplets due to pressure applied to ink due to deformation of a piezoelectric body.
An ink droplet ejection mechanism of a thermal inkjet printhead will now be explained in detail. When a pulse current is supplied to a heater including a heating resistor, the heater generates heat and ink near the heater is instantaneously heated up to approximately 300° C., thereby boiling the ink. Accordingly, ink bubbles are generated by ink evaporation, and the generated bubbles are expanded to exert pressure on the ink filled in an ink chamber. As a result, ink around a nozzle is ejected from the ink chamber in the form of droplets through the nozzle.
When the thermal inkjet printhead has a nozzle that leads to poor ink ejection, streak lines are shown in a printed image, thereby degrading print quality. Accordingly, when there is a missing nozzle, the thermal inkjet printhead should prevent print quality degradation by compensating for the missing nozzle with a normal nozzle. To this end, a method of detecting a missing nozzle by monitoring whether ink is normally ejected through nozzles of the thermal inkjet printhead is necessary.